Image forming apparatuses, which record images and the like on recording media, such as paper and cloth, while transferring these recording media, have been conventionally used extensively. In some image forming apparatuses, transfer of a recording medium using a transfer belt (belt transfer system) is employed since the recording medium can be transferred in a rapid and stable manner by this system.
In the belt transfer system, an endless transfer belt is wound around a plurality of transfer rollers, and the transfer belt is fed by rotationally driving these transfer rollers by some power device. Then, a recording medium is fed onto the transfer belt from a supply portion. In an ink jet printer, for example, the recording medium is transferred to an image forming area under a print head, in which an image is formed by discharging ink from the print head and recorded on the recording medium. After the recording operation is performed, the recorded recording medium is discharged from a discharge portion by the transfer belt.
The transfer belt is mostly made of an elastic material in order to facilitate processing of the belt, such as adhesion processing on the surface of the belt for securely holding a recording medium. In the case of a large image forming area, the transfer belt is required to be long and, therefore, is prone to have deflection or distortion in itself. Then, the recording medium, which is transferred intermittently by the transfer belt, sometimes does not follow the belt or departs from the belt due to inertial force. As a result, the recording medium may also be deflected or positionally displaced by the influence of the deflection or distortion of the belt.
In a commonly used ink jet printer among various image forming devices, recording is performed by ejecting ink in a nozzle of a print head as droplets of ink directly onto the recording medium by means of pressure of a piezoelectric element or thermal foaming. In the vicinity of ink discharge ports of the print head, volatile components such as water in ink evaporate with time, which leads to a drier ink having an increased viscosity. In an on-demand ink jet printer, in which whether or not to discharge ink is determined based on the data to be recorded, especially an ink discharge port with a low frequency of ink discharge will have problems, such as unstable ink discharge from the print head and inability to discharge ink due to an increased viscosity of ink. To avoid these problems, ink discharge called recovery discharge is preformed in addition to ink discharge onto the recording medium so that ink with an increased viscosity can be expelled from the nozzle.
Specifically, in most cases of a serial printer, in which a print head having ink discharge ports arranged in the transfer direction of the recording medium is scanningly moved in a direction perpendicular to the transfer direction of the recording medium so as to record an image for one line, an ink reservoir for recovery discharge is provided close to the position which the recording medium passes such that the print head is moved to the position of the ink reservoir when recovery discharge is to be performed.
With respect to a line printer, in which an elongated print head having ink discharge ports arranged in the width direction of a recording area of the recording medium and recording is performed without scanning movement of the print head, there is known technology in which the entire elongated print head is moved to a position not facing the transfer belt in order to perform recovery discharge. However, such movement of the print head takes a long time period, which makes it impossible to take advantage of high speed printing without scanning movement of the print head.
The below-mentioned Patent Document 1 includes disclosure that an opening of a size corresponding to the width of ink discharge of a print head is provided in a transfer belt and that recovery discharge of the print head is performed at the position of the opening in order to solve these problems.
When an opening such as a hole is provided in a transfer belt, however, there is another problem. Specifically, since the belt is distorted or deflected around the opening due to stress concentrated around the opening, a recording medium cannot be properly held, and therefore the recording medium may be separated from the transfer belt or deflected.
[Patent Document 1]
Publication of Unexamined Japanese Patent Application No. 2001-287377